By Knorr, P. Nakutnyy, P. Luo, Saskatchewan Research Council
Saskatchewan was ranked first in Canada, and fourth in the world, for petroleum exploration and development investment potential, according to the Fraser Institute’s 2016 Annual Global Petroleum Survey. Much of the petroleum exploration and production activities take place in the province’s unconventional oil reservoirs located In the Western Canadian Sedimentary Basin (WCSB), in formations such as Bakken/Exshaw, Viking, Cardium, and Lower Shaunavon.
In general, tight oil reservoirs are characterized by large local variations in permeability, lithology, and mineralogy. Because of the micro- to nano-meter-scale flow channels in tight oil formations, their phase behaviour and multi-phase flow could be significantly different from those in conventional oil reservoirs. While new tight oil wells are highly productive when stimulated through hydraulic fracturing, this production declines rapidly from its initial peak, at rates sometimes in excess of 85% per year and with ultimate primary recovery of only 3 to 10% of the original oil in place.
Innovation related to multi-stage hydraulic fracturing in horizontal wells has proven to be the key factor of the boom in the development of the light and tight oil fields over the last decade. Technology advancements enable oil producers to increase recovery factors while lowering decline rates, capital and operating costs. Even in the current price environment, light and tight oil formations are among the most economic oil plays in North America. However, many gaps remain and significant work is needed to grow or even sustain the current level of production.
Improved and Enhanced oil recovery (IOR and EOR) and well stimulation technologies are needed to maintain and grow the production from the WCSB and to boost the economic value of tight oil reservoirs in general. Enhanced waterflooding and gas flooding (particularly using CO2 and ethane) are considered the two most promising technologies at this time, and have been piloted in some light and tight oil fields in Saskatchewan and in the U.S., along with the implementation of a few innovative variations. However, mature EOR technologies encounter new challenges upon being applied in tight oil reservoirs. Most significant challenges include limited injectivity, poor reservoir contact, exacerbated relative permeability effects (water or gas saturation blocking), high chemical adsorption and water sensitivity due to large surface area and high clay content (particularly in the Viking formation), and difficulty in reservoir and fracture mapping and characterization. This is further complicated by fluid flow and mass transfer between the matrix and fractures with extreme permeability contrast.
In addition, in the current oil pricing environment, efficiency improvement and facility/operation cost saving are projected to be the key focus areas for the petroleum industry over the next few years. This creates a significant need for new innovative EOR solutions in the tight oil formations. Such solutions may include the development of the novel chemical additives, adjusting ionic composition of the water, cyclic hybrid processes and improvements in fracking patterns to optimize them for subsequent EOR processes, as well as the potential introduction of completely new processes. Collaboration between various institutes and operators will be one of the keys to achieving these much-needed improvements in a timely matter.